Where should we use "has/have been" and "had been"? What is the difference between them?

Where should we use "has/have been" and "had been"? What is the difference between them?

Both forms express perfect aspect, that is to say they express a state resulting from an earlier event. The has/have been form is known as the present perfect and relates what has happened in the past to what is happening now. The had been form is known as the past perfect and pushes the events further back. It relates what happened at some time in the past to the situation at some other time in the past. If I say I have been at work for eight hours, I describe the position now. If I say I had been at work for eight hours, I describe the position as it was at some earlier time.